# Hand Calcs for Temperature Drop Through Pipe

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 June 13, 2007, 00:57 Hand Calcs for Temperature Drop Through Pipe #1 Tim Guest   Posts: n/a I would like to use some combination of hand calculations to determine the temperature drop through a hydraulic line. The hydraulic line is sitting in -40°C ambient air. The hydraulic fluid is flowing through the line at ~3m/s and the inlet temperature is known to be 70°C. I would like to find the outlet temperature given a specific length of the line. I know the material properties of the line and the fluid properties. Thanks for any help you may be able to provide.

 June 13, 2007, 01:15 Re: Hand Calcs for Temperature Drop Through Pipe #2 Ahmed Guest   Posts: n/a Introduction to heat transfer, Vedat Arpaci

 June 13, 2007, 08:37 Re: Hand Calcs for Temperature Drop Through Pipe #3 Tim Guest   Posts: n/a Thank you. Unfortunately, I don't have access to that particular book right now - I am going to order it, but likely won't have it until next week. Is there any way you could let me know the basic equations/approach to use? Thanks again.

 June 13, 2007, 11:15 Re: Hand Calcs for Temperature Drop Through Pipe #4 Ananda Himansu Guest   Posts: n/a Free pdf of heat transfer book http://web.mit.edu/lienhard/www/ahtt.html There are three thermal resistances on the heat transfer path: external natural ("free") convection from the air to the solid material (metal?) of the pipe, conduction through the wall of the pipe, and internal forced convection from the pipe wall to the hydraulic fluid. The conduction through the pipe wall may be negligible unless the wall is very thick or the material of the wall is insulative. Find the appropriate equations in the book. For the convection you will need to look at the graphs (or equations) of dimensionless correlations. For e.g., for forced convection, from the graph find the Nusselt number given the calculated Reynolds number. You may have to integrate these relations along the pipe length, or you could use a crude approximation that the wall of the pipe is at a constant temperature (which needs to be calculated based on conservation of energy). If the book contains an advanced example solution, solving a problem similar to yours, then you are in luck.

 June 13, 2007, 16:16 Re: Hand Calcs for Temperature Drop Through Pipe #5 Ahmed Guest   Posts: n/a If you have access to a spread sheet like excell, you can do the following: Take a differential element of the pipe, carry on an energy balance: Energy IN - Energy Out = Energy lost Energy In = m(dot)xCx Tin Energy Out = m(dot)xcxTout Energy Lost through conduction (pipe wall + insulation) and Energy lost through convection = hA(Tsurf-Tambient) Remember both Tsurf and Tout are unknowns, you can guess Tsurf, find Tout and then reiterate untill you reach the right Tsurf Good luck

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